1. Field of the Invention
The present invention relates to a display device, and particularly, to a liquid crystal display device.
2. Description of the Related Art
Recently, liquid crystal display (hereinafter, called “LCD”) devices have better image quality due to the improvement of liquid crystal materials and the development of fine pixel processing techniques. Further, LCD devices are light, thin and have low power consumption. The range of applications for LCD devices is increasing. An LCD device includes a liquid crystal display (LCD) panel, a driving circuit unit for driving the LCD panel and a backlight unit for supplying light to the LCD panel. The LCD panel has liquid crystal cells arranged in a matrix format. More particularly, the LCD panel has liquid crystal cells between two glass substrates (i.e., upper and lower substrates). Each of the liquid crystal cells includes a switching device (i.e., TFT array) for switching signals supplied to the liquid crystal cells. A driving circuit unit is connected to a printed circuit board for driving the LCD panel. The LCD panel is mounted on a member together with the backlight unit, to thereby form an LCD device.
FIGS. 1 and 2 are plan views illustrating an LCD panel mounted on a member. More particularly, FIG. 1 is a plan view of the related art liquid crystal display device, and FIG. 2 is a cross-sectional view of the related art liquid crystal display device taken along line I-I′. As shown in FIG. 1, an LCD device 1 includes an LCD panel 10 and a backlight unit 15 disposed under the LCD panel 10 for supplying light to the LCD panel 10. Meanwhile, a driving circuit unit (not shown) for driving the LCD panel 10 is connected to one side of the LCD panel 10.
The LCD panel 10 and the backlight unit 15 are mounted on a mold frame 20. The LCD panel 10 and the backlight unit 15 are fixed to the mold frame 20 by a top case 19 compressing an edge of an upper surface of the LCD panel 10 and coupled with the side of the mold frame 20. A bottom cover 17 for supporting and protecting the mold frame 20 is provided under the mold frame 20.
The backlight unit 15 includes lamps for generating light. An optical sheet is positioned over the lamps for efficiently supplying the light generated from the lamps to the LCD panel 10. The optical sheet includes a light guide plate, a diffusion plate and prism sheets.
The LCD panel 10 is constructed by attaching a color filter substrate 10a to a thin film transistor substrate 10b with a cell gap therebetween. Liquid crystal molecules are positioned in the cell gap. Polarization plates 13a and 13b are attached to both surfaces of the LCD panel 10.
A color filter and a black matrix are formed on the color filter substrate 10a. A transparent electrode 11 is formed at the rear surface of the color filter substrate 10a. The transparent electrode 11 discharges static electricity that accumulates on the LCD panel 10 to the outside. The transparent electrode 11 is connected to the top case 19 and the bottom cover 17 by a conductive tape 18. Accordingly, the static electricity generated at the LCD panel 10 is supplied by the conductive tape 18 to the top case 19 and the bottom cover 17, which are grounded.
A common electrode and a pixel electrode for generating an in-plane field and driving liquid crystal molecules are formed on the thin film transistor substrate 10b. In the alternative, the common electrode may be formed on the color filter substrate 10a. In this case, the liquid crystal molecules are controlled by a vertical electric field generated between the pixel electrode and the common electrode. The LCD device displays an image by driving the liquid crystal molecules according to signals applied to the pixel electrodes.
In general, liquid crystal molecules can be driven within a temperature range of −20° C. to 60° C. Thus, when an LCD panel is used with a temperature outside of the temperature range of −20° C. to 60° C., an image cannot be normally displayed. For example, if an LCD panel is used in as a display for an airplane, it may not be possible to normally display an image in an environment below −20° C.
When the LCD panel is driven in a low-temperature environment (below −20° C.), the movement of the liquid crystal molecules is slow and thus the screen can not be normally driven. However, after a certain period of time, normal driving is possible. This is because heat generated from the backlight is transmitted to the LCD panel, thereby increasing the temperature of the liquid crystal molecules. Accordingly, since a temperature range in which liquid crystal molecules can be driven is limited in the related art, an image can not normally be displayed in a very low temperature state, which is outside the normal temperature range for driving an LCD panel.